Methods for determining the angle-of-rotation position of a shaft of an internal combustion engine are known. Particularly in the case of a crankshaft, the determination of the angle-of-rotation position is of great importance since important processes in the operation of the internal combustion engine, for example fuel injection or the generation of an ignition spark, are usually individually controlled for each cylinder as a function of the crankshaft angle. For determining the angle of rotation, it is known, for example, to arrange incremental sensors on the crankshaft and/or camshaft. These are normally sensor disks or sensor wheels having incremental markers which in interaction with a sensor arranged in a stationary mount with respect to the engine block allow for the angle-of-rotation position of the crankshaft to be determined. These incremental markers on the sensor disk often take the form of a series of teeth and tooth interstices, and the transitions between tooth and interstice or between interstice and tooth, that is the tooth faces, are detected by a sensor. Known in this respect is also the creation of an enlarged tooth interstice, a so-called gap, by eliminating at least one tooth, with the aid of which the absolute angle of the shaft can be ascertained while the engine is rotating.
The knowledge of the angle-of-rotation position can also be used advantageously for improvements in a restart of the internal combustion engine. If the angle-of-rotation position is already immediately known when the engine is started—and not only after determining the absolute angle with the aid of the gap—then the restart of the engine can be significantly accelerated, with positive effects on comfort and exhaust gas emissions. Particularly in the case of motor vehicles that have an automatic start-stop system, optimal engine restarts are very important. An automatic start-stop system is normally used for fuel saving purposes, the internal combustion engine being switched off if there is no power requirement (for example when coasting or stopping) and the engine being automatically turned on again if it is to supply power (for example when driving off again). Since in this context the engine is regularly restarted, the precise knowledge of the angle-of-rotation position has a significant advantage in the operational management of the internal combustion engine.
An added difficulty in determining the angle-of-rotation position is the fact that normally the engine oscillates when it is turned off, that is, there are alternating movements in both directions of rotation until the engine comes to a standstill. This oscillation primarily arises when the inertia of the engine is no longer sufficient to move the piston in a cylinder against the pressure building up in the cylinder and across the top dead center. The pressure in the cylinder pushes the piston back, thereby changing the engine's direction of rotation, until a counterpressure has built up in another cylinder, which again changes the direction of rotation, or until the engine comes to a final standstill. Simple sensors at the crankshaft are unable to register the direction of rotation and are hence also unable to detect an oscillating movement of the engine.
As a solution, the related art, for example German Patent No. DE 199 00 641, provides an absolute angle sensor at the camshaft, with which the absolute position of the crankshaft can be inferred at any time. Disadvantageous in this regard, however, are the higher costs and the increased space requirement as well as the complex signal processing. In addition, tolerances in the toothed belt can result in deviations between the crankshaft position expected on the basis of the camshaft position and the actual crankshaft position. Another solution is the arrangement of two sensors that are offset by an angle difference of a “multiple of a tooth plus half a tooth”. Disadvantages, however, are the additionally required space, the costs for integrating the second sensor as well as the required narrow tolerances between the two sensors and the sensor wheel.
The systems according to the related art have the common feature that they are able to ascertain the angle-of-rotation position only by detecting tooth faces. This is disadvantageous particularly if, while the engine is decelerated, the sensor detects the beginning of the gap, yet the engine comes to a standstill before the gap has been traversed. Hence there is now uncertainty as to what extent the gap has been traversed and thus what angle-of-rotation position the shaft finally assumed.